The invention relates to a controlled oscillator is used in, for example, a stereo decoder of a television apparatus.
Typical baseband composite audio stereo signals include a main signal formed from the sum of the left and right channel signals (L+R), a pilot signal having a frequency .omega..sub.p which is greater than the maximum frequency of the (L+R) signal, and a difference signal (L-R) which is the difference between the left and right channel signals. The difference signal is in the form of a double sideband, amplitude modulated suppressed carrier centered at a frequency of twice .omega..sub.p. The pilot signal is essential for demodulating the suppressed carrier to extract the (L-R) audio information.
The demodulated (L-R) signal will nominally include a component corresponding to the pilot signal, and the maximum signal frequency of the (L+R) signal is nominally relatively close to the pilot signal frequency.
In such stereo decoder, a phase-lock-loop circuit (PLL) may be used for generating, for example, a signal at the frequency 2x.omega..sub.p that is synchronized to the pilot signal and that is used demodulating the (L-R) signal.